Acoustic wave filter comprising a reflector having an oblique slit
An acoustic wave filter includes a piezoelectric substrate, an IDT (interdigital transducer) formed on the piezoelectric substrate, and reflectors located at both sides of the IDT and composed of electrode fingers, at least one of the electrode fingers of at least one of the reflectors including at least one gap within a propagation path of an acoustic wave.
Latest Taiyo Yuden Co., Ltd. Patents:
This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-059813, filed on Mar. 10, 2008, the entire contents of which are incorporated herein by reference.
FIELDThe present invention generally relates to acoustic wave filters, and more particularly, to an acoustic wave filter having a piezoelectric substrate on which an IDT (interdigital Transducer) and reflectors are formed.
BACKGROUNDThere has been an increasing demand for downsizing, weight lighting and operable frequency raising in portable mobile communication devices due to advance of information-oriented society. A compact and light acoustic wave filter is used to meet the increasing demand. Particularly, an increasing number of portable phones adopt a system in which the transmission frequency and the reception frequency are close to each other. It is thus required to realize greater attenuation at frequencies close to the pass band.
An exemplary acoustic wave filter is a surface acoustic wave filter in which an IDT composed of comb electrodes and reflectors are provided on a piezoelectric substrate. Power is applied to a SAW element and an acoustic wave is thus excited. The SAW filter is capable of processing a radio signal in the range of 45 MHz to 2.0 GHz. The SAW filter is used to form a transmission bandpass filter or a reception bandpass filter.
When an electric signal is applied to the double-mode SAW filter, the acoustic waves are excited by the IDTs and are propagated in a direction perpendicular to the direction in which the electrode fingers extend. The acoustic waves are converted into electric signals of frequencies of the acoustic waves. The reflectors 8 and 10 function to confine the acoustic waves propagated from the IDTs 2, 4 and 6 by utilizing reflection, so that the acoustic waves can be suppressed from being attenuated. Actually, the reflectors 8 and 10 reflect acoustic waves (spurious waves) outside of the pass band. The spurious waves are superimposed and degrade the out-of-band attenuation of the double-mode SAW filter.
As illustrated in
According to an aspect of the present invention, there is provided an acoustic wave filter including: a piezoelectric substrate; an IDT (interdigital transducer) formed on the piezoelectric substrate; and reflectors located at both sides of the IDT and composed of electrode fingers, at least one of the electrode fingers of at least one of the reflectors including at least one gap within a propagation path of an acoustic wave.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
Referring to
It is possible to vary the configuration depicted in
A second embodiment has an exemplary configuration in which the reflectors 8 and 10 have electrode fingers each having multiple gaps.
Referring to
A third embodiment has an exemplary configuration in which two double-mode SAW filters are connected.
In the configurations shown in
The third embodiment having the reflectors each having one slit may be varied so that each reflector can be configured as in the case of the first or second embodiment.
Fourth EmbodimentA fourth embodiment is based on an experiment directed to computing the amount of attenuation while changing the number of gaps of a single double-mode SAW filter.
Each of the reflectors 38 and 40 has the reflection attenuating regions B. In each of the reflectors 38 and 40, the reflection region A has 20 electrode fingers, and the reflection attenuating region B has 18 electrode fingers. The aperture length W1 of the electrode fingers of IDTs 31, 32, 33 and 34, that is, the width of the SAW propagation path is 158 μm.
As described above, a large amount of attenuation can be obtained by forming one gap in each of the electrode fingers of the reflectors, as compared to the arrangement in which no gap is formed in each electrode finger. Further, the attenuation can be increased by forming two gaps in each of the electrode fingers of the reflectors.
Fifth EmbodimentA fifth embodiment is based on an experiment directed to computing the attenuation of double-mode SAW filters connected in parallel in which the electrode fingers of the reflectors have gaps, and to computing the attenuation of double-mode SAW filters connected in parallel in which the electrode fingers of the reflectors have no gaps.
Each of the reflectors 8, 10, 18 and 20 has the reflection attenuating region B. In each of those reflectors, the reflection region A has 30 electrode fingers, and the reflection attenuating region B has 42 electrode fingers. The width W2 of the SAW propagation path is 83 μm.
As described above, the gaps formed in the electrode fingers of the reflectors increase the amount of attenuation in the double-mode SAW filters connected in parallel.
Sixth EmbodimentA sixth embodiment is based on an experiment directed to computing the amount of attenuation while changing the number of slits in the reflectors.
Each of the reflectors 8 and 10 has the reflection attenuating region B. The reflection region A has 30 electrode fingers, and the reflection attenuating region B has 27 electrode fingers. Each of the reflectors 18 and 20 has a reflection attenuating region D. The reflection region C has 30 electrode fingers, and the reflection attenuating region D has 24 electrode fingers. The SAW propagation path in the double-mode SAW filter 100 has a width W3 of 56 μm, and the SAW propagation path in the double-mode SAW filter 110 has a width W4 of 18 μm.
As described above, one slit formed in each reflector increases the amount of attenuation. Two slits formed in each reflector further increase the amount of attenuation.
The first through sixth embodiments are the exemplary double-mode SAW filters. The present invention is not limited to these double-mode SAW filters but includes acoustic wave filters other than the double-mode SAW filters and boundary acoustic wave filters.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various change, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Claims
1. An acoustic wave filter comprising:
- a piezoelectric substrate;
- an IDT (interdigital transducer) formed on the piezoelectric substrate; and
- reflectors located at both sides of the IDT and composed of electrode fingers,
- at least one of the electrode fingers of at least one of the reflectors including at least one gap within a propagation path of an acoustic wave,
- wherein the electrode fingers of the at least one of the reflectors have gaps so that the gaps of neighboring electrode fingers form an oblique slit with respect to a direction of propagation of the acoustic wave and the oblique slit is in at least a part of one of the reflectors.
2. The acoustic wave filter according to claim 1, wherein the at least one of the electrode fingers of the at least one of the reflectors includes multiple gaps within the propagation path of the acoustic wave.
3. The acoustic wave filter according to claim 1, wherein the electrode fingers of the reflectors are not connected in the path of the acoustic wave and have an open electrode.
4. The acoustic wave filter according to claim 1, wherein the electrode fingers of the at least one of the reflectors have gaps so as to form multiple oblique slits with respect to a direction of propagation of the acoustic wave.
5. The acoustic wave filter according to claim 4, wherein the oblique slits cross the direction of propagation of the acoustic wave at different angles.
6. The acoustic wave filter according to claim 1, wherein the electrode fingers of the reflectors include multiple gaps within the propagation path of the acoustic wave.
7. The acoustic wave filter according to claim 1, wherein the electrode fingers of the reflectors have gaps so as to form an oblique slit in each of the reflectors with respect to a direction of propagation of the acoustic wave.
8. The acoustic wave filter according to claim 7, wherein the oblique slits in the reflectors cross the direction of propagation of the acoustic wave at different angles.
9. The acoustic wave filter according to claim 1, wherein the electrode fingers of the reflectors have gaps so as to form oblique slits in each of the reflectors with respect to a direction of propagation of the acoustic wave.
10. The acoustic wave filter according to claim 9, wherein the oblique slits in the reflectors cross the direction of propagation of the acoustic wave at different angles.
11. The acoustic wave filter according to claim 1, wherein the electrode fingers become shorter as the electrode fingers are farther away from the IDT.
12. The acoustic wave filter according to claim 1, wherein the acoustic wave filter is a double-mode surface acoustic wave filter.
13. The acoustic wave filter according to claim 1, wherein the acoustic wave filter includes multiple double-mode acoustic wave filters cascaded.
14. The acoustic wave filter according to claim 1, wherein the acoustic wave filter includes multiple double-mode acoustic wave filters connected in parallel.
15. An acoustic wave filter, comprising:
- a piezoelectric substrate;
- an IDT (interdigital transducer) formed on the piezoelectric substrate; and
- reflectors located at both sides of the IDT and composed of electrode fingers,
- at least one of the electrode fingers of at least one of the reflectors including at least one gap within a propagation path of an acoustic wave,
- wherein the electrode fingers of the reflectors have gaps so as to form an oblique slit in each of the reflectors with respect to a direction of propagation of the acoustic wave, and
- wherein the oblique slits in the reflectors are not mirror symmetrical with each other in a direction perpendicular to the direction of propagation of the acoustic wave.
16. An acoustic wave filter, comprising:
- a piezoelectric substrate;
- an IDT (interdigital transducer) formed on the piezoelectric substrate; and
- reflectors located at both sides of the IDT and composed of electrode fingers,
- at least one of the electrode fingers of at least one of the reflectors including at least one gap within a propagation path of an acoustic wave,
- wherein the electrode fingers of the reflectors have gaps so as to form oblique slits in each of the reflectors with respect to a direction of propagation of the acoustic wave, and
- wherein the oblique slits in the reflectors are not mirror symmetrical with each other in a direction perpendicular to the direction of propagation of the acoustic wave.
3970970 | July 20, 1976 | Worley |
4267534 | May 12, 1981 | Tanski |
4340834 | July 20, 1982 | Sato |
4623855 | November 18, 1986 | Bulst |
4760360 | July 26, 1988 | Grassl et al. |
5621364 | April 15, 1997 | Ruile et al. |
6900577 | May 31, 2005 | Takamine |
7012480 | March 14, 2006 | Nakamura et al. |
20040169568 | September 2, 2004 | Yip et al. |
20060214748 | September 28, 2006 | Funami et al. |
59-207719 | November 1984 | JP |
62-202610 | September 1987 | JP |
07-131291 | May 1995 | JP |
7-240658 | September 1995 | JP |
10-261935 | September 1998 | JP |
11-168350 | June 1999 | JP |
2000-196399 | July 2000 | JP |
2001-127586 | May 2001 | JP |
2001-156577 | June 2001 | JP |
2001-285012 | October 2001 | JP |
2004-266826 | September 2004 | JP |
2004-343259 | December 2004 | JP |
2005-198020 | July 2005 | JP |
- B. Wall et al.; “Balanced Driven Transversely Coupled Waveguide Resonator Filters”; 1996 IEEE Ultrasonics Symposium Proceedings; vol. 1, pp. 47-51, San Antonio, TX, Nov. 3-6, 1996.
Type: Grant
Filed: Mar 4, 2009
Date of Patent: Nov 1, 2011
Patent Publication Number: 20090224854
Assignee: Taiyo Yuden Co., Ltd. (Tokyo)
Inventors: Kouta Ohkubo (Yokohama), Yasufumi Kaneda (Yokohama)
Primary Examiner: Barbara Summons
Attorney: Chen Yoshimura LLP
Application Number: 12/397,719
International Classification: H03H 9/64 (20060101); H03H 9/25 (20060101);